The present invention relates to a method for surface treatment and working of pieces made of titanium or a titanium alloy by dipping the work piece into an alkali bath.
Parts made of titanium have become increasingly important in many fields of engineering, particularly and for example in the field of aircraft engineering and construction. Such a material has a very low specific weight and high strength and is, therefore, superior to other materials, even at high temperatures. Despite these advantages, it cannot be said that the utilization of titantium work pieces pose no problems. The aforementioned advantages are offset to some extend by a low wear resistance, by a strong tendency for stress corrosion and by difficult surface properties concerning adhesion to organic material. Therefore, it is necessary to pretreat these work pieces so that they can be worked at all, and can be used without the aforementioned drawbacks.
For treating or pretreating parts of titanium, it is known to use an acid bath or an alkali bath. This way one can remove portions of the material by etching. Alternatively, one may work such titanium parts through depositing or coating or by means of diffusion welding, or on a utilization of adhesive bonding.
In the case of an acid bath, one usually means hydrofluoric acid or blends with hydrofluoric acid. However, this is a very dangerous material, and its utilization is more and more abandoned. Moreover, the disposal of spent hydrofluoric acid baths is subject to very strict legal requirements rendering their utilization uneconomical in the first place. As far as alkali dipping methods are concerned, basically two types of baths are used. One type of bath has become known under the trade name "Turco 5578." The other method uses a blend of sodium hydroxide and hydrogen peroxide. The first mentioned bath, however, is suitable only for short periods of time for treatment, for example, as a preparation for a bonding or adhesive process. This is so because if a titanium part is treated in "Turco 5578" for a longer period of time than necessary for such pretreatment, one obtains an undesired coating. The second type of alkali bath permits longer treatment times, but the content of such a bath is basically instable, so that this particular method requires a rather large extent of maintenance, supervision and control.